1. Field of the Invention
The present invention relates to an apparatus for testing high speed electroplating to which a Hull cell test tank is applied.
2. Prior Art
At present, plating is applied on the surface of a metal in various fields in daily life. Plating is required to be carried out in a plating bath having a composition suitable for the plating to be carried out under the optimal electrodeposition conditions of current density, agitation speed, temperature of the plating liquid, etc. Usually, even if plating is started under optimal conditions, the composition of the plating bath is gradually changed as plating is continued. Moreover, predicted impurities and unexpected impurities are incorporated, leading to a change in the characteristics of a plated film to be required.
Accordingly, it is required for constantly obtaining the best plated film to maintain the optimum bath composition and electroplating conditions at all times. According to the change in the composition of the plating liquid, the addition of chemicals, removal of the impurities, adjustment of the various conditions such as current density are required in addition to the prediction of change in the bath composition. Consequently, it is necessary to well understand the conditions of fresh plating liquid and the conditions of the plating liquid which is now used.
For understanding the conditions of the plating liquid, chemical analysis such as titration or instrumental analysis such as ion chromatographic analysis is carried out. Further, a plating test method, which is called a Hull cell test, has been widely used for total research of the characteristics of plating liquid, and observation of the states of electroplating as well as examination and management of the bath composition of the presently used plating liquid and electrodeposition conditions.
FIGS. 4 and 5 show the testing apparatus for use in the Hull cell test.
FIG. 4 shows a tank to be used in the Hull cell test. The tank 20 is formed so that the horizontal section is a trapezoid. On the oblique side 22 and the vertical side 22 of the trapezoid, a cathode plate 23 and an anode plate 24 are placed, respectively. The tank is filled with an electrolyte 25. The characteristic of the tank 20 is to place the cathode plate 23 inclined to the anode 24 so that the distance between one end of the cathode plate 23 and the anode plate 24 is different from the distance between the other end of the cathode plate 23 and the anode 24. Accordingly, when plating is carried out in an electric circuit as shown in FIG. 5, there are differences in the cathode current densities at both ends of the cathode plate 23. As a result, the state of the deposition of plate at every cathode current density can be observed on one test piece. From the test piece (cathode 23) obtained by the test, the total research of the characteristics and the total observation of the states of the plating liquid in the electroplating can be carried out and, at the same time, the bath composition of the plating liquid and the conditions of the electrodeposition can be examined and managed.
Usually, in the case where electroplating is carried out using a new plating liquid at the beginning the Hull cell test is carried out with the previous conditions to understand the characteristics of the plating liquid, and then the optimum electrodeposition conditions for obtaining a desired plated film, such as the range of the current density, the range of the temperature, and stirring conditions are examined.
When a new plating tank, a new power supply, or the like is placed, the design of the equipment is carried out according to the optimum conditions based on the results of the previous Hull cell test in some case, but the conditions of the plating equipment which has been already used is simulated by the Hull cell test in many cases. In this case, the optimum conditions are groped by changing the temperature conditions or adding a chemical as occasion may demand.
Moreover, by carrying out the Hull cell test utilizing a plating liquid before use and the plating liquid after use, respectively, the proportion of change in the plating liquids before use and after use can be examined. This makes it possible to predict the bath composition of the plating liquid which will be changed in the future under the conditions and the states of the plated film.
However, in the conventional Hull cell test, the test is carried out in a stationary state of the cathode plate 23 of the substance to be plated or even if the cathode plate 23 is reciprocated by relatively moving the plating bath by means of a reciprocating device, the reciprocation speed in the Hull cell test is at most approximately 5 m/minute. What is more, the Hull cell test can only test the electroplating operated at several Amps over a period of several minutes. Consequently, the Hull cell test is disadvantageous in that it is applicable to testing neither plating of electric parts called hoop plating, which has been popularized in recent years nor high speed electroplating, which is carried out by continuously plating wires produced from an iron factory or an electric wire maker at a high speed. To be specific, high speed electroplating is a method of instant plating at a high current as high as several Amps times ten by moving a substance to be plated at a high speed, which is at most 120 m/minute. Accordingly, in order to simulate such a state, a large-sized testing apparatus is required and, thus, the conventional Hull cell test which utilizes a small sized and simple apparatus cannot be applied.